1. Field of the Invention
This invention relates generally to inside and outside diameter gages, and more particularly to diameter gages which provide an accurate reading of the + or - tolerance of the inside or outside diameter of flexible rings and/or generally round objects by applying controlled pressure to and measuring the interior or exterior circumference of the object and converting the measurement of the circumference to a diameter through a lever and indicator mechanism constructed on a ratio of 3.1416 to 1 (the ratio of the circumference to the diameter).
2. Brief Description of the Prior Art
In the past, there has been no reliable apparatus or method for accurately measuring the outside diameter of flexible rings and/or oval or out-of-round objects. These objects, such as O-rings and seals are usually molded of rubber, teflon, and similar materials. The control of the quality of the finished product is usually accomplished by certifying the mold prior to accepting molded O-rings, seals, and the like.
The standard practice for measuring the inside diameter of flexible rings, seals, etc., is by the use of a conical tapered gage which has a series of vertically spaced circles scribed on its circumference corresponding to various diameters. A ring or seal to be measured is placed on the conical tapered gage and allowed to rest where its inside diameter engages the exterior of the conical surface and a reading to determine the diameter on the gage at which the ring is at rest.
There are several patents which disclose various gages and ring testing apparatus.
Thornton U.S. Pat. No. 2,290,605 discloses a testing machine for testing split lock-washers which utilizes a split core to exert a uniform gradually increasing pressure to the inside periphery of the washer until it ruptures to determine the structural strength of the washer.
Bartlett U.S. Pat. No. 3,111,840 discloses a hydraulic tensile tester for ring structures which utilizes hydraulic pressure to exert a uniform gradually increasing pressure to the inside periphery of a ring until it ruptures to determine the modulus of elasticity and ultimate tensile strength of the ring.
Dega et al U.S. Pat. No. 3,628,376 discloses a test instrument for determining uniformity in molded elastomeric rings wherein the ring is flexed between two power driven rollers while being loaded at a predetermined deflection by a third roller connected to a load sensor coupled to an instrument which records the stress level about the circumference of the ring.
Rober U.S. Pat. No. 4,122,705 discloses a ring inspection device wherein a pair of crossed mandrels are moved into the center of the ring and spread apart to stretch the ring in a twisted path. The mandrels are rotated so that the angular orientation of the cross section changes as the ring passes an optical measurement apparatus which senses the cross section diameter of the ring at several locations while a load cell senses the elasticity of the ring.
The present invention is distinguished over the prior art in general, and these patents in particular by a gage apparatus for determining uniformity in the inside or outside diameter of flexible rings and generally round objects based on the ratio of the circumference of a circle to its diameter. A spring biased lever pivotally mounted on a support plate has a releasable clamp at one end. An indicator is engaged with the lever to indicate the amount of pivotal movement thereof. A thin flexible band of stiff material has one end secured to a spool on the support plate and a portion of its length passes slidably through the clamp and forms a circular loop and its terminal end is fixed to the clamp. The ratio of the distance from the pivot point of the lever to the connection with the band is pi (3.1416) times the distance from the pivot point to the connection with the indicator whereby circumferential measurements are converted and indicated as diametric measurements. As the lever pivots, the diameter of the circular looped portion of the band will increase or decrease.
The looped portion of the band is set to engage the circumference of a master ring of known diameter and then the clamp is tightened to secure the band to the lever and the indicator is set to zero. The master ring is then removed and the band is engaged on the circumference of an object to be measured. The lever will pivot corresponding to the changes in the circumference between the master ring and the object being measured, such that the difference between the known diameter and the diameter+of the object being measured will be indicated.